The present invention generally relates to air cooling of a motor using a radially mounted fan.
The fundamental requirement of the cooling of an electric machine is to achieve the required removal of heat so that the temperature distribution resulting from the losses associated with the energy conversion does not result in component temperatures that exceed the component thermal capability. The temperature distribution varies with the operating conditions of the motor, duty cycle, and environmental conditions including type of cooling. Cooling may be addressed with passive and active cooling methods. Passive cooling includes natural convection, radiation, and thermal conduction to the mounting structure. Active cooling includes forced air and forced fluid cooling. Active cooling may be applied to the internal components and external structure of the electric machine. A major requirement of a cooling system applicable to traction applications is to be contamination resistant due to harsh environment at such an installation. The significant components requiring proper thermal management are the windings of the electric machine, bearings, magnets, and touch surfaces.
Methods typically employed for cooling electric machines depend on the type of machine and include open, drip-proof and protected machines. These machines are physically open to the atmosphere such that convection occurs between the internal motor components and ambient. Shields and guards are often provided to prevent direct access or contact with the motor components.
Totally enclosed machines, however, are not open to ambient. This is primarily for protection against the environment. Heat rejection from these machines is accomplished with conduction to the structure and outer enclosure convection only, since the interior of the machine is not accessible to external cooling.
Totally enclosed forced ventilation machines are encapsulated machines typically with an external fan providing forced air over the motor housing. Cooling fins and channels are often used to direct the coolant flow and improve the heat transfer from the machine housing to the cooling medium. Liquid cooling can also be used for this type of machine.
Installations typical to aerospace and transportation applications require coordinated packaging and layout of the machine to conform with the space and envelope restrictions of the vehicle. In this architecture, the fan is typically shaft mounted and the coolant is forced axially over the machine outer housing. Nonetheless, whether the fan is electrically or mechanically driven, axial space is consumed by the fan and is, therefore, not available for the main electric machine.
Therefore, a need exists in the aerospace industry for an air cooling of a variable speed motor using a radially mounted fan.